1. Field of the Invention
The present invention relates to improvements in a thermo-magnetic recording device wherein a magnetized latent image is produced on a magnetic layer.
2. Discussion of the Prior Art
There is known a thermo-magnetic recording device wherein a latent image is produced on a magnetic layer made of a ferromagnetic material, by locally heating the ferromagnetic layer. Commonly, this type of printer utilizing a thermo-magnetic recording technique uses a magnetic layer which is magnetized in the same direction over its entire recording area. The latent image is formed by reversing the direction of magnetization at individual local printing spots on the magnetic layer. The reversal of the magnetizing direction is accomplished by utilizing a residual magnetism which is obtained by first heating the magnetic layer to an elevated temperature near the Curie Point and then cooling the heated layer down to the room temperature in a magnetic field. This method of magnetization utilizing the residual magnetism after heating of the magnetic recording medium requires a reduced energy to produce the magnetic field to which the medium is exposed for reversed magnetization, as compared with the method wherein the magnetic medium is not heated prior to exposure to a magnetic field. Moreover, the former method assures substantially saturated magnetization of the recording medium by the residual magnetism.
For locally selectively heating the magnetic layer as a recording medium, it is considered to use a laser or xenon beam which is converged on a desired printing spot on the magnetic layer. However, this method requires an expensive, intricate optical system which includes a light source and a converging lens.
An alternative method of locally heating a magnetic recording layer is known, which uses a thermal printing head having a multiplicity of heat-generating elements arranged on a substrate. In this arrangement, a latent image is produced on the magnetic layer by selectively energizing the heat-generating elements while the thermal printing head is moved on the layer. An example of a magnetic recording device adapted to practice the above method is disclosed in Japanese Patent Application No. 55-18472 which was laid open in 1981 under Publication No. 56-115278 the subject matter of which is disclosed in U.S. Pat. No. 4,442,441 to Kikuchi et al. This device is capable of forming a latent image on a magnetic layer, with a relatively simple construction without an optical system.
However, the magnetic recording device using such a thermal printing head as indicated above suffers from accumulation of heat in the thermal printing head, which limits the frequency at which current pulses are applied to the heat-generating elements. Therefore, the rate of forming the latent image on the magnetic layer is accordingly limited. Since an overheat of the thermal printing head results in the failure to correctly form the latent image, the electric energy to be applied to the printing head must be limited. Hence, the operating efficiency of the recording or printing device is lowered.